The present invention relates generally to digital radio communication and more specifically to a noise detection circuit for noise measurement and/or local oscillator frequency control.
In radio receivers, a noise detection circuit is provided for operating a squelch circuit to prevent production of unwanted signal. Such noise detection circuits are currently designed for detecting thermionic, or white noise from analog baseband signals. However, the prior art noise detection circuit is not suitable for detecting noise from digital baseband signals due to the fact that the quality of a digital baseband signal is not only determined by the white noise but by intersymbol interference which is primarily caused by phase variations during transmission. This is particularily acute when the signal is affected by noise impulses or interfered with unwanted signals.